Variable artificial transmission lines



E. LOVICK, JR

VARIABLE ARTIFICIAL TRANSMISSION LINES Jung 28, 1960 2 Sheets-Sheet 1Filed May 16, 1955 IN V EN TOR.

EDWARD LOVICK JR.

Agent June 28, 1960 Filed May 16, 1955 E. LOVICK, JR

VARIABLE ARTIFICIAL TRANSMISSION LINES 2 Sheets-Shqet 2 IN V EN TOR.

EDWARD LOVICK JR.

M Agent United States Patent VARIABLE ARTIFICIAL TRANSMISSION LINESEdward Lovick, Jr., Van Nuys, Calif., assignor to Lookheed AircraftCorporation, Burbank, Calif.

Filed May 16, 1955, Ser. No. 508,741

3 Claims. c1. ass-29y.

This invention relates to variable electrical four-terminal networks andmore particularly to a variable artificial transmission line elementwhich simulates, within wide limits, any combination of inductance andcapacitance for phase shifting or impedance matching purposes.Basically, the artificial line includes two elements each having adielectric insulating tube with a number of conducting patches or platesmounted on the outer surface thereof. The conductive patches serve asone plate ofa variable capacitor. Conductive wires or strips connectadjacent conductive patches and form a series inductance circuit whichspirals around the outside of the dielectric tube. A cam-likesemi-cylindrical conductive rotor is slidably carried within thedielectric tube forindependent rotational movement causing asimultaneous increase in shunt capacitance and series inductancedepending upon the direction of rotor rotation from an intermediateposition.

The transmission line element may be designed so that the ratio betweeninductance and capacitance is constant and, therefore, 'thecharacteristic impedance may be specified and made independent of rotorposition.

An object of this invention is to provide a variable artificialtransmission line element which may be used as a variable phase shifterby matching the input impedance with the characteristic impedance of theelement. 7

.Another object of this invention is to provide a variable artificialtransmission line element which may be used as a coupling device forimpedance matching an antenna or the like with microwave transmitting orreceiving equipment.

Another object of this invention is to provide a variable artificialtransmission line element which may be used as a piece of test apparatusto determine the optimum transmission line electrical characteristicsfor communications equipment.

Another object of this invention is to provide a variable artificialtransmission line-element for either balanced or unbalanced lines whichhas negligible power losses and which is substantially unaffected byextreme environ-- mental conditions or aging.

Still another object of this invention isto provide a variableartificial transmission line element which is rugged in constnlction andeconomical to manufacture.

Further and other objects will become apparent from a reading of thefollowing detailed description especially when considered in combinationwith the accompanying drawing wherein like numerals refer to like parts.

in the drawing:

Figure 1 is a fragmentary perspective view showing the constructiondetails of the unbalanced li'ne version of the variable artificialtransmission line;

Figure 2 is a sectional side view of one of the variable artificialtransmission line elements shown in Figure 1;

Figure 3 is a schematic block diagram showing the electricalfour-terminal coupling network for the variable artificial transmissionline elements of Figure 1; t

Figure 4 is a schematic block diagram showing a typical 7 application ofthe variable. artificial transmission line ole electrical couplingnetwork for the variable artificial transmission line elements of Figure5.

Referringto Figure 1 a pair of variable artificial transmission lineelements 1 and 2 are carried within a shielding, box-like container 3'.Elements'l and 2 are electricallyisolated from one another by apartition'4' which is suitably secured to the walls 'of' the container.

Each variable artificial transmissionline element]. and 2 includes atubular member 5 of dielectric material asshown in Figures '1 and 2 anda plurality of curved 'or semi-cylindrically shaped conductive plates 6secured 'to the outer surface of the dielectric tube such as by bondingwith an adhesive. The plates are equally spaced axially of the tube on alongitudinal segment thereof and in alignment with one another. orstraps 7 are connected at each end to adjacent plates 6 by wrapping thewire around the outside of tube '5 as best shown in Figure 1 to form aspiralling seriescircuit. Solder 8 or other suitable means may be usedto provide the electrical connectionbetweenpl-ates 6 andiwires 7'. Plate9 at one end 10 of tube 5 connects with a terminal socket 1 1 throughlead 12. Terminal socket '11 is carried by housing 3 for electricallyconnecting the variable artificial transmission line with an externalcircuit such as is schematically illustrated in Figure 4. Plate 13adjacent the opposite end 14 of tube 5 connects with the correspondingplate 15'on the other variable artificial transmission line element 2through lead 16. Plate 17, the last transmission line elements, providesa wide range of inductance and capacitance in a versatile four-terminalor L network for accomplishing any of a number of functions such asthose enumerated in the statement of the objects.

Dielectric tube 5 ofeach variable artificial transmission line element 1and 2 is suitably restrained against rotation relative to container 3 byconnections with terminal posts 11 and 19 as well as by spring-likebrackets 21 carried on the inside of the container.

' A core or rotor 22 having a pair of cylind'rically shaped end portions23 and 24 and a semi-cylindrically shaped center portion 25, as mostclearly shown in.Figure 2, is provided for each variable artificialtransmis-' sion line element. Rotor 22 is slidably received withindielectric tube 5'. Cylindrically shaped end portions 23 and 24 of rotor22 serve to support and align the rotorwith respect to the dielectrictube and. position the curved surface of the rotor closely adjacent alongitudinal segment of the inner surfaceof the dielectri'ctube. Whilecenter portion 25;- of the rotor is shown and described herein as beingsemi-cylindrical, it should beiunderstood' that any cross-sectionalshape may be employed so long as acam-like action is efiectivelyobtained to provide means forvarying the inductance and capacitance ofthe external circuit. A 7 f Shafts 26 and 27, one at each end of rotor22 extends 7, 2,943,276 Patented June 28 1960 A plurality of conductivewires 7 through openings such as openings 28 and 29 in container 3 toprovide the primary means of support for each variable artificialtransmission line element. A knob 30 secured to shaft 27 exteriorly ofcontainer 3 provides a convenient means for positioning rotor 22relative to plates 6 and wires 7.

Rotor 22 serves to control both the inductance and capacitance of theplate and wire arrangement surrounding the outside of dielectric tubes5. When semi-cylindrical center portion 25 of the rotor is moved byrotor rotation to a position adjacent plate 6 and spaced from wire 7both a high capacitance and high inductance will be obtained. When rotor22 is rotated to the opposite position wherein the semi-cylindricalcenter portion 25 is spaced a maximum distance from plates 6 andadjacent wires 7 both the capacitance and inductance of the circuit willbe at a minimum. Intermediate rotational positions of rotor 22 willresult in providing inductance and capacitance values which are betweenthe maximum and minimum values obtained by the two extreme rotorpositions described above. Both the inductance and capacitance varydirectly and simultaneously so that the ratio therebetween may be madeconstant for all rotor positions wherein the variable artificialtransmission line elements may be designed having a fixed characteristicimpedance.

The upper and lower limits of capacitance and inductance of eachtransmission line element will depend upon the size and number. ofplates 6, the diameter and thickness of dielectric tube and upon thelength of wires 7 as well as upon the particular type of materials used.All of these factors should be considered when designing an element tomeet the performance requirements of a given case. i

Figure 4 schematically illustrates a typical application of the variableartificial transmission line described above wherein the unit shown inFigure 1 is connected in series with an antenna 31 and ireceiver 32 forimpedance matching purposes. By simply rotating rotors 22 through knobs30 to introduce the desired amount of inductance and capacitance intothe circuit the impedance of the antenna may be matched with that of thereceiver to increase the effective signal strength and thereby improvereceiver operation. As previously set forth the artificial transmissionline may also be used as a phase shifter or as a piece of test apparatusto determine the optimum impedance for a coupling network.

The variable artificial transmission line element configuration shown byFigures 1 through 3 is applicable to unbalanced transmission lines only.Where the device is to be used with balanced transmission lines a slightmodification of the circuitry is required as shown in Figure 5 wherein apair of plates 33 and 34 are substituted for each of the plurality ofplates 6 in the Figure 1 configuration. Thus in the balanced lineversion of the transmission line elements, two separate circuits may beprovided on the outside of dielectric tubes 35. Induction wires orstraps 36 connect the corresponding plates together to furnish the twinlead type of coupling illustrated in Figure 6. The construction ofcontainer 39 and the means for supporting elements 37 and 38 issubstantially identical to the construction shown and described inconnection with Figure l.

The balance line version of the variable artificial transmission lineelements as shown in Figures 5 and 6 operates to provide a wide range ofinductance and capacitance through rotation of knobs 40 in the samemanner as was described for the unbalanced line version of Figure 1. Itis particularly useful as an impedance matching device for televisionreceiving or transmitting equipment where balanced line circuitry iscommonly employed.

It is to be understood that certain alterations, modifications andsubstitutions may be made to the instant disclosure without departingfrom the spirit and scope of the invention as defined by the appendedclaims.

I claim:

l. A variable artificial transmission line having a substantiallyconstant characteristic impedance comprising, a pair of tubulardielectric members, a series of semicylindrical conductive platessecured to one semi-cylindrical portion of the outer wall of each saiddielectric member, said conductive plates being spaced apart and axiallyaligned with one another, a plurality of helical inductive wire segmentsconfined to the other longitudinal semi-cylindrical portion of the outerwall of each said dielectric member and having their opposite endselectrically connecting adjacent conductive plates forming a singlecontinuous electrical circuit spiralling around each said dielectricmember, a conductive core, generally semi-circular in cross section,rotatably carried within each dielectric member, means for rotating eachconductive core, and means electrically connecting the continuouselectrical circuits formed on said tubular members in parallel wherebythe inductance and capacitance of the circuit may be varied in a directrelationship over a' wide range by rotation of the conductive cores.

2. A variable artificial transmission line element comprising, a tubulardielectric member, a plurality of spaced, semi-cylindrical conductiveplates secured to one longitudinal semi-cylindrical portion of the outerwall of said dielectric member and aligned with each other axially ofthe dielectric member to serve as one side of a variable capacitor, aplurality of inductive wire segments confined to the other longitudinalsemi-cylindrical portion of said dielectric member and having theiropposite ends electrically connecting adjacent conductive plates andforming with said plates a continuous circuit spiralling around saidtubular dielectric member for conducting electrical energy, and aconductive semicylindrical core rotatably carried within said tubulardielectric member and closely adjacent the inner wall of said memberwhereby to simultaneously vary the inductance and capacitance of thecircuit while maintaining a nearly constant characteristic impedance.

3. A variable artificial transmission line element comprising, a tubulardielectric member, a plurality of pairs of; spaced semi-cylindricalconductive plates secured to one longitudinal semi-cylindrical portionof the outer wall of said dielectric member and aligned with each otheraxially of the dielectric member to serve as one side of a variablecapacitor, a plurality of inductive wire segments confined to the otherlongitudinal semi-cylindrical portion of said dielectric member andelectrically connecting alternate conductive plates together to form apair of continuous electrical circuits spiralling around said tubulardielectric member for conducting electrical energy, and a conductivesemi-cylindrical core rotatably carried within said tubular dielectricmember and closely adjacent the inner wall of said member whereby tosimultaneously vary the inductance and capacitance of the electricalcircuits while maintaining a nearly constant characteristic impedance.

References Cited in the file of this patent UNITED STATES PATENTS887,526 Germany Aug. 24,

